Osteoporosis, the loss of cortical and trabecular bone predisposing to fractures, is a major public health problem that affects approximately 20 million individuals and is an underlying cause of 1.3 million new fractures per year among persons over age 45 in the United States. Postmenopausal osteoporosis is multifactorial in etiology, involving both hereditary and environmental factors. A family history of osteoporosis has been cited widely as a risk factor despite little evidence to substantiate this view. Previous studies have yielded conflicting results, possibly due to small sample sizes, the combining of pre- and postmenopausal mothers with premenopausal daughters, and the measurement of bone density being confined largely to the appendicular skeleton. The objectives of this proposed project are 1) to estimate the extent of familial resemblance in bone density and bone architecture between mothers and daughters; 2) to determine whether mothers with low bone density have daughters with low bone density; and 30 to determine the extent of familial resemblance in bone density between the nuclear and extended families of the Baltimore Longitudinal Study of Aging (BLSA). These objectives will be accomplished through a cross-sectional study of mothers who are enrolled in the Study of Osteoporotic Fractures (SOF) and their daughters as well as the families of the BLSA. Initially, familial correlation of bone density between male and female participants (mothers, fathers, daughters, sons, siblings) of the BLSA will be evaluated. Additionally, bone density measurements of the hip, forearm and calcaneus, ultrasound measurements of the calcaneus, anthropometric and muscle strength measurements of approximately 500 mother-daughter pairs in the Baltimore center of the multi-site Study of Osteoporotic Fractures (SOF) will be utilized to estimate familial correlation. If familial correlation can be demonstrated for bone density and bone architecture, it may be possible to identify daughters at a relatively young age with an elevated risk of osteoporosis and fractures and initiate preventive measures before bone is lost.